Many animal viruses have been proven to be oncogenic not only for the natural host, but also for other animals and bird species. In fact, many viruses which have been non-pathogenic in the original animal reservoir have been proven to be oncogenic when transferred to other animals. The question arises whether such viruses could also be oncogenic for man. A population of veterinarians would have an excessively high risk of exposure to sick animals and has had proven animal infections through such exposures. A study of veterinarians might reveal an increased risk of mortality from cancer in general or from a specific type of malignancy such as leukemia or lymphoma. The graduates of ten of the older veterinary schools in the U.S. will be followed through alumni records, directories of the American Veterinary Medical Association, and obituary notices in the journal of the Association. A life-table analysis of the mortality experience by cohorts of graduation years will be compared for specific causes of death to that of physician specialists, including radiologists, and U.S. white male populations. The mortality rates from leukemia and lymphoma are of particular interest since the specific type of lymphoma or cell type of leukemia may differentiate a risk from radiation exposure versus exposure to animal viruses.